By Raj Jayavant · Updated
Playing an instrument is a motor skill, and motor skills are learned by repeating a movement accurately. Repeating it inaccurately also teaches something, just not what you wanted. Your hands do not know which repetitions were the good ones.
Slowing down does two things. It gives you time to make the correct movement rather than an approximation of it, and it gives you time to notice what you are doing while you do it. At tempo, a difficult passage happens faster than you can pay attention to it, which is precisely why it is difficult.
The useful rule is not a number, it is a test: start at the fastest tempo where you can play the passage accurately, with no hesitation, three times in a row.
In practice that often lands near half speed, which is why half speed is the number most often quoted. But it depends on the passage and on you. If you are making mistakes, it is still too fast, and it does not matter how slow that means. Some passages need a quarter speed to start with, and there is nothing wrong with that.
The mistake to avoid is choosing a tempo that feels respectable rather than one where you play accurately. Slow practice only works if it is actually slow enough.
Around ten percent per step. Small enough that each increase feels almost unnoticeable, large enough that you get somewhere.
The point of small increments is that you should never be practicing at a tempo you cannot play. Every repetition should be a correct one. Big jumps mean spending time at a speed where you fumble, which is the thing the whole method exists to avoid.
The same test as before: three clean repetitions in a row. Not one lucky one. Three, consecutively, with no hesitation and nothing approximated.
If you get two clean and fumble the third, that counts as zero. This sounds harsh and it is the part that makes the method work, because it stops you from advancing on the strength of a repetition that happened to go well.
You will hit a tempo where the passage falls apart. The instinct is to keep playing it at that speed until it improves. It will not. You are practicing the failure.
Drop back to the last speed where you were clean, play it a few more times, and try the increase again. Often the second attempt succeeds because the extra repetitions at the lower tempo were what you actually needed.
Most advice on this assumes a metronome, which works when you are reading from notation. It does not help when you are learning from a video or a track, which is how most people learn now. For that you need to slow the recording itself.
Two things make it practical. The audio has to stay in the same key when you slow it, or you cannot play along. And the passage has to repeat without you reaching for the mouse every twenty seconds, because stopping to rewind breaks exactly the concentration you are trying to build.
PhraseLoop does both: mark the passage once, set the speed anywhere from a quarter to double, and it loops on its own with the pitch unchanged. Raise the speed a step when the passage is clean, without losing your markers.
Less than you would expect. Three clean repetitions and move on. Long stretches at one speed feel productive and mostly build tolerance for that speed rather than progress towards the next.
Short daily sessions beat long occasional ones by a wide margin. Twenty minutes a day for a week will get you further than three hours on a Sunday, because the consolidation happens between sessions, not during them.
If a passage is failing because of a fingering choice, a technique you have not learned, or an instrument set up badly, slow practice will not rescue it. It will just make the wrong solution very reliable.
Before starting the tempo ladder, play the passage once very slowly and ask whether the movement itself is sensible. Fix that first. There is more on diagnosing this in how to practice a difficult passage.